The algae, known as sea lettuce, is common in oceans around the world and is eaten by a number of animals, including humans. It's harmless to the water and sea life in normal quantities, but blooms like the one in Qingdao can interfere with regular sea life. Worse than that, when the stuff starts to rot as it washes up on the beach, it produces hydrogen sulfide, the toxic gas that gives bad eggs their familiar odor. In a similar, but much smaller-scale, event in France several years ago the fumes were responsible for several deaths.

Biologists studying the phenomenon have yet to determine why the annual bloom in the Yellow Sea has reached gargantuan proportions, although the finger of suspicion points to nutrients in fertilzer-rich agricultural runoff and wastewater. This washes out to sea where it teams up with castoffs from seaweed farms along the coast of Jiangsu Province.

Algal blooms aren't limited to oceans, as those living near the Great Lakes know. There was a massive bloom of 'blue-green algae' on Lake Erie in 2011 — the largest on record, covering nearly a fifth of the lake's surface — and similar conditions (warm temperatures combined with fertilizer washing off farms during heavy spring rains) are expected to contribute to a bumper crop in the lakes again this summer. Blue-green algae is a very different beast than what China is seeing, though.

Whereas 'sea lettuce' is just annoying to us when it's in the water and only potentially dangerous to us when it washes up on shore and rots, blue-green algae — also called cyanobacteria — is dangerous between 50-70% of the time (depending on exactly which species are present in the water). Swimming in the water, drinking it, or even eating fish taken from the lake can make someone seriously ill. Not only that, even when it doesn't directly impact on our health, massive blooms consume all the oxygen in the water, devastating the populations of fish and other life in the lakes.

(Photo courtesy: Getty Images)

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